1

UNIVERSITY OF NAIROBI

Biogas production potentialfrom coffee pulp

Gatomboya wet coffee factory

MWAKESI MWALILI GEOFFREY

F16/2337/2009

SUPERVISOR

ENG. KANDIE M. KIPKOROS

A project submitted as a partial fulfillment of the requirement for the

award of the degree of

BACHELOR OF SCIENCE IN CIVIL AND CONSTRUCTION

ENGINEERING

2014

2

Abstract

Coffee processing done by wet and dry methods discard away alot of the biomass generated by

the coffee plants at different stages from harvesting to consumption. This includes cherry wastes,

coffee parchment husks, sliver skin, coffee spent grounds, coffee leaves, and wastewater. Wet

processing uses up to 15 m3of water to produce one ton of clean beans and for every ton of beans

produced, about one ton of husks are generated. It is estimated that coffee processing is

generating about 9 million m3 of wastewater, and 50,000 tons of husks annually in the

Kenya.(George Tchobanoglous, et al).

Energy from coffee waste is in form of biogas that is used as an alternative energy on the wet

method process for extraction of coffee beans from coffee cherries. During the wet method

process enormous amounts of waste water is generated in the form of pulp and residual water.

This waste water is high in organic matter and acidity content and with a Chemical Oxygen

Demand value that varies between 18000 and 30000 milligrams per litre. The waste water is used

to produce biogas as an alternative energy.(Antier, P., A)

Kenya is a major producer of coffee in East Africa. Among the areas where coffee farming and

production is done is at Karatina town in Nyeri County. This research was carried out with

Gatomboya wet coffee mill in Karatina as the focus of the case study.

The main aim of this project research was to get the biogas potential of coffee wastewater

through COD and BOD tests and the BOD/COD ratio used to determine that.

A lack of a bio digester at Gatomboya wet coffee mill and lack of necessary resources however

made it impossible to get the actual amount of biogas that can be produced from say 1m3 of

wastewater. This was the major limitations of this project.

3

Dedication

I dedicate this piece of work to Almighty God. For from him, through him, and to him are

allthings to him be glory forever‼ Amen.

4

Acknowledgement

First of all I would like to praise the Almighty God for his endless opportunity and help

thatenabled me to continue my education and complete this research work successfully.

I am particularly grateful to my advisors Eng. KandieKipkoros for his constructive advice,

guidance, encouragement, willingness to supervise my research and their valuable comments

from early stage ofproposing the research work to the final thesis research results write up.

Therefore, I wouldlike to extend my deepest gratitude to him for his continuous technical support

andcommitment during the whole course of this research work.

My appreciation also goes to the University of Nairobi, College of Architecture and Engineering,

School of Engineering, Department of Civil and Construction Engineering for giving me the

opportunity to partake my undergraduate degree at such a prestigious institution of learning and

excellence.

I would also like to thank Gatomboya wet coffee factory situated in Karatina, for their allowance

for me to use the factory as their base area for case study and for their hospitality during my

visits there.

My deepest thanks and appreciation goes to MungaShadrack and Kelvin Ojwando for their

inputs in this joint project has enable its completion.

5

Table of Contents Abstract ......................................................................................................................................................... 2

Dedication ..................................................................................................................................................... 3

Acknowledgement ........................................................................................................................................ 4

Table of contents…………………………………………………………………………………………………………………………………… 5

Table of tables ............................................................................................................................................... 7

Table of figures ............................................................................................................................................. 8

Acronyms ...................................................................................................................................................... 9

Chapter 1 ........................................................................................... Ошибка! Закладка не определена.0

1.0 Introduction ............................................................................................................................... 100

1.1 Background and rationale for the proposed project .................................................................. 100

1.2. Statement of the problem ................................................................................................................. 13

1.3. Goal and Objectives ......................................................................................................................... 13

1.3.1. Specific Goals and Objectives .................................................................................................. 14

1.4. Brief approach methodology ............................................................................................................ 14

1.5. Limitations of study ......................................................................................................................... 14

Chapter 2 ..................................................................................................................................................... 15

2.0 Literature review ............................................................................................................................... 15

2.1. General ............................................................................................................................................. 15

2.2Coffee Production and Processing ..................................................................................................... 16

2.2.1 The importance of coffee .............................................................................................................. 16

2.2.2 Coffee plant ................................................................................................................................ 17

2.2.3.Coffee fruit ..................................................................................................................................... 17

2.3.Biogas ............................................................................................................................................... 21

2.3.1. Potential for biogas in kenya ..................................................................................................... 22

2.3.2. Background to Anaerobic Digestion ......................................................................................... 22

2.3.3. Anaerobic Gigestion process .................................................................................................... 23

2.3.4. Characterization of substrates in biogas production .............................................................. 25

2.4. Biogas production from coffee pulp. .......................................................................................... 26

2.4.1. Anaerobic digestion of coffee pulp .......................................................................................... 27

6

2.5 Information needed for biogas potential from coffee wastewater..................................................... 27

2.5.1 Biological Oxygen Demand ....................................................................................................... 28

2.5.2 Chemical Oxygen Demand ........................................................................................................ 30

Chapter 3 ..................................................................................................................................................... 31

3.0 Materials and methodology ............................................................................................................... 31

3.1. Fieldwork ......................................................................................................................................... 31

3.1.1. Reconnaissance ......................................................................................................................... 31

3.1.2. Descriptions of the Experimental Site....................................................................................... 32

3.1.3. Site Visitation ............................................................................................................................ 32

3.1.4. Sample Collection ..................................................................................................................... 35

3.2. Methodology and materials for determination of BOD of the sample ............................................. 35

3.3. Methodology and materials for determination of COD of the sample ............................................. 38

Chapter 4 ..................................................................................................................................................... 40

4.0 Results, analysis and discussion........................................................................................................ 40

4.1 BOD results and analysis .................................................................................................................. 40

4.1.1 Results ........................................................................................................................................ 40

4.2 COD results and analysis .................................................................................................................. 41

4.2.1 Results and analysis ................................................................................................................... 41

4.3 BOD/COD ratio (biodegradability, αs) ............................................................................................. 42

4.4 Discussion ......................................................................................................................................... 42

Chapter 5 ..................................................................................................................................................... 43

5.0 Conclusion and recommendations .................................................................................................... 43

5.1 Conclusion ........................................................................................................................................ 43

5.2 Recommendation .............................................................................................................................. 43

REFERENCES ........................................................................................................................................... 44

APPENDICES ............................................................................................................................................ 47

7

Table of tables

Table 2.1 Potential methane yield, heating oil equivalent, electricity production and installed

capacity from coffee wastes in Kenya .......................................................................................... 20

Table 2.2 Typical biogas composition .......................................................................................... 21

Table2.3Possible installed electric capacities for major biogas potentials considered in this study

………22

Table 2.4 Characteristics (mean values) of solid agro-industrial wastes for anaerobic digestion 25

Table 2.5 Characteristics (mean values) of agro-industrial wastewaters for anaerobic digestion 26

8

Table of figures

Figure 2.1 Coffee fruit ................................................................................................................................ 17

Figure 2.2 Coffee processes ........................................................................................................................ 19

Figure 2.3 Bioas model diagram ................................................................................................................ 23

Figure 2.4Biological and chemical stages of Anaerobic Digestion……… … ……………………………………….24

Figure 3.1Grading coffee berries and the cherry hopper .................................................................... 32

Figure 3.2Pulping machine ........................................................................................................................ 33

Figure 3.3Coffee pulp separated ................................................................................................................ 33

Figure 3.4 Fermentation tank ..................................................................................................................... 34

Figure 3.5Drying cables ............................................................................................................................. 34

Figure 3.6 Recirculation pump house ......................................................................................................... 35

Figure 3.7 Soak pit ...................................................................................................................................... 35

9

Acronyms

AD Anaerobic Digestion

CO2 Carbon dioxide.

CSTR Continuous Stirred Tank Reactor

CWS Coffee Washing Stations

CWP Coffee Wet Processing

DM Dry Matter

EA Eastern Africa.

FAS Ferrous Ammonium Sulphate

FM Fresh Matter

GHG Green House Gases

GSC Gas Solid Chromatography

GW Gigawatt

KWh Kilowatt-hour

MWh Megawatt-hour

VS Volatile Solids

UASB Up-flow Anaerobic Sludge Blanket

10

Chapter 1

1.0 Introduction

1.1 Background and rationale for the proposed project

In the 20th century, the world economy has been dominated by technologies that depend on

fossilenergy, such as petroleum, coal, or natural gas to produce fuels, chemicals, materials and

power. The continued use of fossil fuels to meet the majority of the world‟s energy demand is

threatened by increasing concentration of CO2 in the atmosphereand concerns over global

warming. The combustion of fossil fuel isresponsible for 73 % of the CO2 emission (Wildenborg

and Lokhorst, 2005).

The heightened awareness of the global warming issue has increased interest in the

developmentof methods to mitigate greenhouse gases (GHG) emission. Much of the current

effortto control such emissions focuses on advancing technologies. These are; Reduce energy

consumption, Increase the efficiency of energy conversion or utilization, Switch to lower carbon

content fuels,

Enhance natural sinks for CO2, and Capture and store CO2.

Reducing use of fossil fuels would considerably reduce the amount of CO2 produced, as well as

reduce the levels of pollutants. As concern about global warming and dependence on fossil fuels

grows, the search for renewable energy sources that reduce CO2emissions becomes a matter of

attention.

Interest in alternative transportation fuels are growing due to oil supply insecurity and its

impending peak, and the imperative to lower GHG emissions from fossil fuel use in order to

stave off adverse global climatic changes. The main contributors to air pollution are vehicular

emissions of GHG and particulate matter. Renewable energies are essential contributors to the

energy supply portfolio as they contribute to world energy supply security, reducing dependency

of fossil fuel resources, and providing opportunities for reducing emissions of GHG. Energy

security and climate change imperatives require large-scalesubstitution of petroleum-based fuels

as well as improved vehicle efficiency.

Replacing petroleum with biofuel can reduce air pollution, improve rural economies by creating

job opportunities and raising farm incomes, diversify energy portfolios, minimize dependence on

foreign oil and improve trade balances in oil-importing nations. To reduce the net contribution

11

ofGHGs to the atmosphere, bioethanol has been recognized as a potential alternative to

petroleum derived transportation fuels and cooking fuels.Biomass is a potential renewable

energy source that could replace fossil energy for transportation. Biomass is solar produced

organic matter such as wood, agricultural byproduct energy crops such as fast-growing trees and

grasses, municipal wastes, paper mill sludge and living-cell materials (algae, sewage, etc).

Biomass is naturally plentiful and renewable. Coffee pulp is also among the potential biomass

resources for bioethanol production.

Biorefining of waste biomass involving the integrated production of chemicals, materials

andbioenergy is a potential alternative for adding significant economic value to the waste as a

bioresource. In the21st century and beyond, bio-resource based economy is envisaged globally as

a strategy towards achieving social, economic and environmental sustainability. Agriculture will

be core to the bio-resource basedeconomy, providing source of raw materials, which are

sustainable, plentiful and inexpensive for utilizationin bioprocesses for the production of bio

products. In the Eastern Africa‟s (EA) economy, agriculture is themainstay and currently

accounts for about 80% of the rural incomes, and coffee is among the important cash crops. East

Africa is currently producing about 600,000 tons of coffee beans annually. Crop production and

processing activities are generating huge quantities of organic

waste.(http://en.wikipedia.org/wiki/Coffee#World_production)

Coffee processing done by wet and dry methods discard away 99% of the biomass generated by

thecoffee plants at different stages from harvesting to consumption. This includes cherry wastes,

coffeeparchment husks, sliver skin, coffee spent grounds, coffee leaves, and wastewater. Wet

processing uses up to15 m3 of water to produce one ton of clean beans and for every ton of beans

produced, about one ton ofhusks are generated. It is estimated that coffee processing is

generating about 9 million m3 of wastewater, and600,000 tons of husks annually in the East

Africa region (Adams, M.R. and J. Dougan. 1987.)

The increasing rate at which fossil and residual fuels are releasing CO2 into the atmosphere has

raised international concern and has led to intensive efforts to develop alternative, renewable,

sources of primary energy.

12

The solar energy stored in chemical form in plant and animal materials is among the most

promising alternative fuels not only for power generation but also for other industrial and

domestic applications on earth.

Biomass absorbs the same amount of CO2 in growing that it releases when burned as a fuel in

any form. The term „biomass‟ refers to all biodegradable organic matter that can be recycled into

energy or returned to soil: agricultural waste and residues or by-products from the food and

beverage industry, sludge from municipal and industrial wastewater treatment plants, wood from

forests and recycling processes, the organic fraction of domestic waste, as well as energy crops,

algae, etc. Biomass contribution to global warming is zero. In addition, biomass fuels contain

negligible amount of sulphur, so their contribution to acid rain is minimal. Over millions of

years, natural processes in the earth transformed organic matter into today's fossil fuels: oil,

natural gas and coal. In contrast, biomass fuels come from organic matter in trees, agricultural

crops and other living plant material. CO2 from the atmosphere and water from the earth are

combined in the photosynthetic process to produce carbohydrates that form the building blocks

of biomass. The solar energy that drives photosynthesis is stored in the chemical bonds of the

structural components of biomass. If we burn biomass efficiently oxygen from the atmosphere

combines with the carbon in plants to produce CO2 and water. The process is cyclic because the

carbon dioxide is then available to produce new biomass.

Unlike any other energy resource, using biomass to produce energy is often a way to disposeof

biomass waste materials that otherwise would create environmental risks. Today, there are

ranges of biomass utilization technologies that produce useful energy from biomass.

• Direct Combustion

• Gasification

• Anaerobic Digestion

• Methanol & Ethanol Production

13

There are a number of challenges that inhibit the development of biomass energy. In this regard,

formulation of sustainable energy policy and strategies in addressing these challenges is of

importance for the development and promotion of biomass energy.

1.2. Statement of the problem

Due to the increase in the price of petroleum, crude and products, and environmental

concernsabout air pollution caused by the combustion of fossil fuels, the search for alternative

fuels has become vital. The use of food crops (like maize) for biofuel production may

causeinflation of cost of these crops leading to food insecurity. To alleviate such problems,

alternative and non-edible agricultural products must be investigated.

The coffee plant, which is indigenous to Kenya, produces coffee fruit (bean) at different seasons

per year. The bean represents about 40 % of the fruit; the other 60 % is generallydiscarded as

waste (pulp and mucilage). Coffee pulp represents the most abundant and nonedibleagricultural

waste obtained after pulping ripe fruit. Kenya is currently producing about 50,000 tons of coffee

beans on average for the past 6 years.(http://en.wikipedia.org/wiki/Coffee#Production). Use of

coffee pulp and other by-products has become a priority incoffee producing countries for

economic, ecological and social reasons.

1.3. Goal and Objectives

The goal of this study is to determine energy production potential / opportunity in coffee waste

biomass (coffee pulp and wastewater)

There are several barriers that need to be overcome in order to promote large-scale biogas and

ethanol use and production in Kenya. The main obstacles for uptake of this technology so far

have been a lack in awareness on the side of potential investors and policy makers about the

viability of biogas as a source of electricity and other sources of energy. There are specific goals

and objectives arising from these barriers.

1.3.1. Specific Goals and Objectives

1. To evaluate the suitability of coffee pulp for biogas production.

14

1.4. Brief approach methodology

1. A field visit to Gatomboya coffee factory in Karatina, Nyeri County

2. Establish sampling points for sample analysis

3. Laboratory testing to determine the biogas potential of the sample

1.5. Limitations of study

The above study is limited only to a small sample size hence problems that may arise due to

large-scale bioenergy production will not be known. Also, large-scale production is less efficient

hence a lesser amount of the biofuel is produced.

In addition, Gatomboya coffee factory mentioned above has no upflow anaerobic sludge blanket

or any biogas reactor that is able to recycle the waste biomass into useful energy for use at the

factory.

15

Chapter 2

2.0 Literature review

2.1. General

In the 21st century, the world economy has been dominated by technologies that depend on fossil

energy such as petroleum, coal, or natural gas for fuels, chemicals, materials and power

production. As concern about global warming due to dependence on fossil fuels grows, increase

in the price of petroleum and crude oil products, the search for renewable energy sources has

becomes a matter of great importance. Replacing petroleum with biofuel can reduce air

pollution, improve rural economies by creating job opportunities and raising farm incomes,

diversify energy portfolios, minimize dependence on petroleum and improve trade balances in

oil-importing nations.

To reduce the net contribution of greenhouse gases to the atmosphere, bioenergy has been

recognized as a potential alternative to petroleum-derived transportation fuels and cooking fuels.

Biomass is a potential renewable energy source that could replace fossil energy for

transportation. The use of food crops for biofuel production may however cause inflation of cost

of these crops leading to food insecurity. To alleviate such problems, alternative and non-edible

agricultural products must be investigated.

Use of biomass from waste and waste water would be a great alternative and as such is the main

objective of this proposed project. This entails refining of waste biomass involving the integrated

production of chemicals, materials and bioenergy, and this is a potential alternative for adding

significant economic value to the waste as a bio-resource. In the 21st century and beyond, bio-

resource based economy is seen globally as a strategy towards achieving social, economic and

environmental sustainability. Agriculture will be core to this bio-resource based economy,

providing source of raw materials, which are sustainable, plentiful and inexpensive for utilization

in process of production of bio-products. In the Kenyan economy for example, agriculture is the

mainstay and currently accounts for about 80% of the rural incomes, with coffee among the

important cash crops. Kenya is currently producing about 50,000 tons of coffee beans on average

for the past 6 years.(http://en.wikipedia.org/wiki/Coffee#Production). Crop production and

processing activities are generating huge quantities of organic waste.

16

2.2 Coffee Production and Processing

Coffee is a brewed beverage prepared from the roasted or baked seeds of several species of an

evergreen shrub of the genus Coffea. The two most common sources of coffee beans are the

highly regarded Coffeaarabica, and the "robusta" form of the hardier Coffeacanephora. The latter

is resistant to the coffee leaf rust (Hemileiavastatrix), but has a more bitter taste. Coffee plants

are cultivated in more than 70 countries, primarily in equatorial Latin America, Southeast Asia,

and Africa. Once ripe, coffee "berries" are picked, processed and dried to yield the seeds inside.

The seeds are then roasted to varying degrees, depending on the desired flavor, before being

ground and brewed to create coffee.

Coffee is slightly acidic pH 5.0–5.( Thecoffeefaq.com (2005-02-16). and can have a stimulating

effect on humans because of its caffeine content.It is one of the most popular drinks in the world.

It can be prepared and presented in a variety of ways. The effect of coffee on human health has

been a subject of many studies; however, results have varied in terms of coffee's relative

benefit.The majority of recent research suggests that moderate coffee consumption is benign or

mildly beneficial in healthy adults. However, the diterpenes in coffee may increase the risk of

heart disease.[Cornelis, MC; El-Sohemy, A (2007). "Coffee, caffeine, and coronary heart

disease". Current Opinion in Clinical Nutrition and Metabolic Care]

2.2.1 The importance of coffee

Coffee is one of the most commercialized commodities worldwide. According to FAO coffee is

among the 20 commodities that generated most money compared to other commodities in 2007.

In total, 5.8 million tonnes were exported worldwide generating a value of 13.7 billion USDX.

The cultivation of coffee is the most important source of income for a large part of the rural

population. During times of harvest (plucking), thousands of families go to the coffee plantations

to offer their cheap labour and in this way earn some money. The coffee industry of Kenya is

noted for its cooperative system of production, milling, marketing and auctioning coffee. About

70 percent of Kenyan coffee is produced by small scale holders. It was estimated in 2012 that

there were about150000 coffee farmers in Kenya and other estimates are that six million

Kenyans were employed directly or indirectly in the coffee industry. The major coffee growing

regions in Kenya are the high plateaus around Mt. Kenya, The Aberdare Ranges, Kisii, Nyanza,

Bungoma, Nakuru, Kericho and Ruwenzori Mountains.

17

2.2.2. Coffee plant

There exists a large variety of coffee plants. However, only two of them have been widely

commercialized: the genus coffea Arabica and coffeaCanephora(commonly known as Robusta).

The first genus is categorized by its slow growth, delicate in growth and with less productivity

rates than the Robusta; it is cultivated in mountainous regions. The high plateaus of Mt Kenya

plus the acidic soil provide excellent conditions for growing coffee plants. The genus Robusta

has higher production rates and it can be cultivated in less mountainous regions than the

Arabica. The latter one characterizes itself for producing a fine and aromatic coffeeXII. Coffee

from Kenya is one of the „mild Arabica‟ type.

2.2.3. Coffee fruit

Figure 2.1 Coffee fruit(Journal of Food Chemistry)

Where;1=centre cut; 2= bean (endosperm) 3= silver skin (testa, epidermis) 4=(parchment

(hull, endocarp) 5=pectin layer 6=pulp (mesocarp) 7= outer skin (pericarp, exocarp).

The fruit or cherry from the coffee, as is shown in the figure above consists of two grains which

face each other with their flat surfaces. The pulp (6) or mesocarp and the external skin (7) or

epicarp covers both grains. Each grain of coffee is covered by 3 layers, from the exterior to

theinterior these are: a layer of pectin (5), parchment (4) or endocarp and the silver skin (3) or

spermoderm. Beneath these layers the green coffee bean is encountered.

The harvest season lasts for approximately 90 days. During this season, the workers (cherry

cutters) spend several days close to the same coffee plant cutting those grains that have matured

(red). After filling one basket of grains they pour the grains in a bag which after being filled is

brought to the mill where the grain is being processed. There are two different methods which

can be used to process the coffee cherries: the dry mill and the wet mill.

18

In the dry mill process, almost exclusively applicable to the genus Robusta, the grains are left in

the open field to be sun‐dried. After the grains have lost almost all their water content (from 65

% to 10-12 %.)After the cherries are dry, they are put through a drymechanical pulping (or

decorticating) process in which the green coffee bean is separated fromthe outer residue material

(skin and husk) of the cherry. The dry process removes the upper hardcover (the husk) and the

inner skin (parchment) in the milling process.

A mass of 100 kg of red cherries picked at 65 % moisture content will result in approximately

40kg of sun-dried coffee cherries delivered to the processing plant. Of this mass, about 17 kg

willbecome sun-dried coffee beans while the remaining 23 kg will end up as residue at

theprocessing plant (http://en.wikipedia.org/wiki/Coffee#Production).

The process in the wet mill begins by bringing the coffee cherries in the previously described

bags (filled by baskets) to a reservoir. From here on the cherries are transported by gravity to the

de‐pulping machines. This step can be enhanced with water, or can be performed dry (more

environmentally friendly) when the reservoir has been designed to this purpose. In Nicaragua,

the transport to the de‐pulping machines is brought forth by water (and gravity). One major

advantage of this method is that dirt, not‐ripe and overripe grains will float on the water surface.

In the de‐pulping machines the cherries are selected based on their size and de‐pulped, which is

the process in which the pulp and the outer skin are removed. There remains a slimy layer around

the coffee bean with a varying thickness of 0.5 to 2 mm.

For 100 kg of ripe cherries delivered to a washing plant, 60 % by mass ends up as washed

coffeepulp with the remaining 40 % consisting of the green bean and endocarp (parchment). Of

this 40% washed coffee cherry, only 20 kg remains after sun-drying of the bean and parchment.

This isthen shipped to the washed coffee processing facility where the parchment isremoved. The

result is 16 kg of washed coffee beans ready for export and 4 kg of parchment asresidues

The average residue production per metric ton of wet red cherry is about 600 kg, i.e. based

ongreen coffee bean production, the residue potential would be 1.4 times the mass of green

beansproduced (ESMAP, 1986). A wet processing result in a better quality of coffee products, as

aresult its share of the market is growing.

Coffee is one of the most important agricultural cash crops in Kenya. It is produced by small

scale farmers, cooperatives and large scale estates. The main harvest season is from October to

December. After harvesting the coffee cherries are mainly processed by wet fermentation to

19

obtain the parchment coffee (dried beans covered by paper-like coating). During this process

large amounts of organic wastes like pulp and wastewater are produced. The pulp can be used as

organic fertilizer. According to the Coffee Research Foundation in Kenya for each ton of

parchment about 2.15 tons of pulp and 80 m3 of wastewater (without recirculation of process

water) are produced. In case of future change to more optimized fermentation methods with

recirculation of process water the amount of wastewater would decrease drastically, but the

amount of COD would be roughly the same.

Figure 2.2Coffee processes

The feasibility of anaerobic digestion of coffee wastes has been documented by many authors but

the biogas yield tends to vary in literature. Hofmann and Baierreported a biogas yield of 380 m3/t

VS (57-66 % methane) from coffee pulp (16.2 % DM, 92.8 % VS) in lab scale batch experiments

and a biogas yield of 900 m3/t VS for semi continuous experiments. Kivaisi and

Rubindamayugireported methane potentials of 650 and 730 m3/t VS of Robusta and Arabica

20

coffee solid waste (mixture of pulpand husks). Different digester designs like CSTR, plug-flow

and two stage systems (CSTR for hydrolysis, UASB for methanogenesis) can be used for the

anaerobicdigestion of solid coffee wastes.

The anaerobic treatment of wastewaters can be done by high performance reactor systems for

wastewater treatment with immobilization of microorganisms. Due to fermentation processes,

sugar compounds in the wastewater are converted into acids, leading to very low pH values in

the wastewater. Thus, neutralization may be necessary before the anaerobic treatment.

The potential of biogas production from coffee wastes in Kenya is as below: according to the

Coffee Board of Kenya 57,000 tonnesofparchment coffee were produced. Because 90% is

processed by wet fermentation inKenya, 51,300 t of parchment coffee are obtained by this

fermentation method.Assuming that each ton of parchment is producing 2.15 t of pulp and 80 m3

of wastewater the total amount of residues would be 145,125 t of pulp and4,104,000 m3of

wastewater per year. Table 2-4 summarizes the potential electricityproduction from coffee

residues in Kenya.

Table 2.1Potential methane yield, heating oil equivalent, electricity production and installed

capacity from coffee wastes in Kenya (Agro-industrial biogas in Kenya)

Methane

yield [m3/a]

Heating oil

equivalent

[tons/a]

Electricity

production

[kWh/a]

Installed

Capacity

[MW]

Min 4,227,000 3,500 12,681,000 2

Max 41,027,000 34,000 147,698,000 18

Mean 22,627,000 18,750 80,189,500 10

21

2.3 Biogas

Biogas typically refers to a mixture of gases produced by the breakdown of organic matter in the

absence of oxygen. Biogas can be produced from regionally available raw materials such as

recycled waste. It is a renewable energy source and in many cases exerts a very small carbon

footprint.

Biogas is produced by anaerobic digestion with anaerobic bacteria or fermentation of

biodegradable materials such as manure, sewage, municipal waste, green waste, plant material,

and crops. It is primarily methane (CH4) and carbon dioxide (CO2) and may have small amounts

of hydrogen sulphide (H2S), moisture and siloxanes.

The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with

oxygen. This energy release allows biogas to be used as a fuel; it can be used for any heating

purpose, such as cooking. It can also be used in a gas engine to convert the energy in the gas into

electricity and heat. (Biogas & Engines, www.clarke-energy.com, Accessed 21.12.13)

Table 2 Typical biogas composition(YishakSebokaet al., 2009)

Compound Chemical formula %

Methane CH4 50 – 70

Carbon dioxide CO2 30 – 49

Nitrogen N 0 – 1

Hydrogen H 0 – 5

Hydrogen sulphide H2S 0.1 – 0.3

Water H2O Saturated

2.3.1 Potentials for biogas in Kenya

The data below is on theoretical potentials from 3 selected groups of biomass available from the

agro-industrial business in Kenya and for municipal solid waste in Nairobi. Since the data is

necessarily incomplete, and since future potentials are not considered, the actual potential could

well be higher. Most promising sectors for electricity production from biogas from anaerobic

digestion are:

22

Table 3 Possible installed electric capacities for major biogas potentials considered in this

study(www.giz.de/facheexpectise/..gtz2010-en-biogas-assessemt-kenya.(Agro-industrial

Biogas in Kenya.)

Potential installed capacity [MW]

Mean Min Max

Municipal solid waste 37.5 11 64

Sisal production 20 9 31

Coffee production 10 2 18

Total all sub-sectors 67.5 22 113

The total potential installed electric capacity of all sub-sectors ranges from 29 to 131 MW,

generating 202 to 1,045 GWh of electricity, which is about 3.2 to 16.4 % of the total Kenyan

electricity production of 6 360 GWh as of 2007/08. The extent of actual realization of this

potential will depend on the incentives provided for investment, in particular the tariff

framework.

2.3.2. Background to Anaerobic Digestion

Anaerobic digestion is the conversion of bio-organic non-woody material, the feedstock (or the

substrate), by micro-organisms in the absence of oxygen into stable and commercially useful

compounds. The process is similar to composting except that composting is aerobic, involving

oxygen in its breakdown of organic matter and does not produce useful energy. AD feedstock is

often unwanted wastes such as slurry or deliberately produced energy crops (such as maize

silage) grown specifically for feeding the AD plant. The products from the digestion process are:

Biogas. This is a mixture of about 60% Methane (CH4), 40% Carbon Dioxide (CO2)

together with trace amounts of other gases. This is then combusted to generate electricity,

heat or used as a road fuel.

23

Digestate (soil conditioner, organic fertilizer). This is an inert and sterile wet product

with valuable plant nutrients, such as ammonium compounds, and organic humus. It can

be separated into liquor and fibre for application to land or secondary processing.

Figure 2.3Bioas model diagram

2.3.3Anaerobic Digestion Process

The concept of anaerobic digestion simply involves putting a load of organic matter into a

warmed airtight container and leaving it for a few days. The microbes in the matter will digest

the non-cellulosic feedstock releasing methane (CH4) and carbon dioxide (CO2). However, it is

more complex than that if the operator is to achieve an efficient performance from the digester.

24

There are 4 key biological and chemical stages of Anaerobic Digestion:

1. Hydrolysis; is the process that breaks down the long chain carbohydrates into simpler

soluble organic compounds (i.e. glycerol). This is the step in AD that takes the longest

therefore it determines the retention time to be held in the digester vessel.

2. Acidogenesis(acid fermentation) bacteria then break the compound down directly into

acetic acid.

3. Acetogenesis. If not broken down directly to acetic acid, it is first broken down to propionic

butyric acid and long chain volatile fatty acids.

4. Methanogenesis; the hydrogen then binds with carbon molecules released from the acid

digestion to make methane.

Hydrolysis Acidogenesis Acetogenesis Methanogenesis

Figure 2.4 Biological and chemical stages of Anaerobic Digestion

Carbohydrate

s

Fats

Proteins

Sugars

Fatty Acids

Amino Acids

Carbonic Acids & Alcohols

Hydrogen Carbon Dioxide Ammonia

Hydrogen Acetic Acid Carbon Dioxide

Methane &

Carbon

Dioxide

Methane&

CarbonDio

xide

25

The biogas product is primarily, 55-65%, Methane (CH4) with the balance being Carbon Dioxide

(CO2) together with some minor gases such as hydrogen sulphide(H2S) and ammonia (NH4) and

some moisture.

2.3.4. Characterization of substrates in biogas production

A list of the substrates and their average characteristics examined in this study is presented in

Table 2-2 for solid substrates and in Table 2-3 for wastewaters. The suitability of different solid

substrates for anaerobic digestion can be expressed by the methane potential per ton of fresh

matter (FM). (DM = dry matter, VS = volatile solid)

Table 2.4 Characteristics (mean values) of solid agro-industrial wastes for anaerobic digestion

Substrate DM

content

[% FM]

VS

content

[% DM]

Biogas

potential

[m3/ton

VS]

Methane

content

[%]

Methane

potential

[m3/ton

VS]

Methane

potential

[m3/ton

FM]

Coffee pulp 20 93 390 63 244 45

Tea waste 78 97 358 55 201 54

Sisal pulp 12 85 523 60 330 37

Source; (Kivaisi A.K)

For wastewaters the methane potentials per m3 of wastewater are much lower compared to solid

substrates due to the low content in organic material and high water content. Values range from

0.7 m3 for nut processing wastewater to 22 m

3 for distillery stillage. Those values may vary

strongly depending on specific technical preconditions of the processing.(Kivaisi A.K).

Table 2.5 Characteristics (mean values) of agro-industrial wastewaters for anaerobic digestion

26

Substrate COD in

wastewater

[g/l]

COD

degradability

[%]

Biogas

potential

[m3/ton

CODrem]

Methane

content

[%]

Methane

potential

[m3/ton

CODrem]

Methane

potential

[m3/ton

FM]

Coffee

processing

wastewater

14.3 90 375 70 265 4.3

Nut

processing

Wastewater

4.3 70 330 75 250 0.7

Distillery

Stillage

90 66 390 73 290 22

Sisal

decortications

wastewater

11.5 87 475 84 400 4.3

Source; (Kivaisi A.K)

The major disadvantage of wastewaters is the low energy density, but considering technical

aspects they are easier to pump and to stir than solid substrates. If wastewaters are used in CSTR

(Continuous stirred tank reactor) biogas plants a large digester volume for the fermentation

process is needed. Thus, wastewaters are treated in customized wastewater treatment systems

like UASB (Up flow anaerobic sludge blanket; the most common system), fluidized bed, fixed

film, sequencing batchetc. Those systems are working with an immobilization of the

microorganisms whereby the retention time and digester volume can be reduced.

2.4. Biogas production from coffee pulp.

The two major waste products from coffee processing, pulp and waste water (80%), can be

utilized to produce sufficient quantities of biogas. This is due to the high content of organic

matter and acidity as evidenced in Central America. The major process of biogas is through

anaerobic process in the pulp and waste water.

It is reported that several successful attempts have been made in the use of coffee pulp for

27

the production of biogas in the process of anaerobic digestion (Boopathy, 1988). It has

been demonstrated that anaerobic digestion of one ton of coffee pulp could successfully

generate about 131m3 biogas the value of which is equivalent to 100 litter of petrol fuel

(Kida et al., 1994). In a case study conducted in Tanzania to study the feasibility of using

different agro-industrial by products for biogas and electric power generation Robusta and

Arabica coffee pulp produced about 650 and 730 m3 methane per ton respectively, which

were found to be highest in comparison to the amount of methane generated by any other

agro-industrial by products studied (sugar filter, sisal and maize bran) showing that coffee

pulp could efficiently be used in the production of biogas.(Kida et al., 1994).

2.4.1Anaerobic digestion of coffee pulp.

Anaerobic waste water treatment is the biological treatment of waste water without the use of air

or elemental oxygen. Organic pollutants are converted by anaerobic microorganisms to a gas

containing methane and carbon dioxide, known as biogas.

Methane is the main constituent of biogas, being responsible for its calorific value. This

workobjective was to present the analysis of methane concentration in the biogas originated from

anaerobic treatment system ofcoffee pulp of coffee wet processing (CWP) at laboratory scale.

The methane concentration wasto be performed by gas-solid chromatography (GSC) analyses.

2.5 Information needed for biogas potential from coffee pulp.

For the calculation of potentials from wastewater the following information is needed:

Amount of coffee pulp (m3 per year)

Chemical Oxygen Demand of coffee pulp

Biological Oxygen Demand of coffee pulp

BOD/COD biodegradability ratio

Methane content in biogas

The lack of data at Gatomboya wet coffee factory regarding the amount of coffee pulp produced

daily or annually and the absence of a biogas reactor hence only makes it possible for biogas

potential to be proven and not calculated.

This is done through the COD, BOD and BOD/COD ratio.

28

2.5.1Biological Oxygen Demand

Biochemical Oxygen Demand (BOD) is the amount of oxygen required by bacteria while

breaking down decomposable organic matter under aerobic conditions. The most widely used

parameter of organic pollution to both wastewater is the 5-day BOD i.e. BOD5. This

determination involves the measurement of the dissolve oxygen used by the microorganisms in

the biochemical oxidation of organic matter. The BOD test results are used to:

i. Determine the approximate quantity of the oxygen that will be required to biologically

stabilize the organic matter present.

ii. Determine the size of waste-treatment facilities.

iii. Measure the efficiency of some treatment processes

iv. Determine compliance with wastewater discharge permits

The BOD test is an empirical bioassay-type procedure which measures the dissolveld oxygen

consumed by bacteria and other microbial life while the organic substances are present in the

solution. The BOD standard test conditions are incubation at 20oC in the dark for a specified

period of time, mostly five days. The reduction in the dissolved oxygen concentration during this

incubation period is a measure of the biochemical oxygen demand and is expressed in mg/l

oxygen or mg/l BOD. The actual environmental conditions of temperature, biological population,

water movement, light conditions and oxygen concentration cannot be accurately reproduced in

the laboratory.

A blank sample of distilled water is usually treated and incubated in the same way as the rest of

the samples as a control. The measurement of the dissolved oxygen can be carried out by the

wrinkler method.

Principle

If sufficient oxygen is available, the aerobic biological decomposition of an organic waste will

continue until all of the waste is consumed. A number of distinctive activities occur. First, a

portion of the waste is oxidized to end products to obtain energy for cell maintenance and the

29

synthesis of a new cell tissue. Simultaneously, some of the waste is converted into new cell

tissue using part of the energy released during oxidation. Finally, when the organic matter is used

up, the new cells begin to consume their own cell tissue to obtain energy for cell maintenance.

This third process is called endogenous respiration. Using the term COHNS – representing the

elements carbon, oxygen, hydrogen, nitrogen and sulphur – to represent the organic waste and

the term C5H7NO2 to represent cell tissue, the three processes are defined by the following

generalized chemical reactions:

Oxidation:

COHNS + O2 – bacteria → CO2 + H2O + NH3 + other end products + energy

Synthesis:

COHNS + O2 + bacteria – energy → C5H7NO2(new cell tissue)

Endogenous respiration:

C5H7NO2 + 5O2 → 5CO2 + NH3 + 2H2O

If only the oxidation of the organic carbon that is present in the wastewater is considered, the

ultimate BOD is the oxygen required to complete the three reactions given above. This oxygen

demand is known as the ultimate carbonaceous BOD.

The BOD test is widely used to determine the “pollution strength” of domestic and industrial

wastes in terms of the oxygen that they will require after being discharged into natural water

systems. It is also important in the design of treatment plants and in monitoring their efficiency.

2.5.2Chemical Oxygen Demand

COD test is a measure of quantity of oxygen required to oxidize the organic matter in a

wastewater sample, under specific conditions of oxidizing agent, temperature and time. COD test

is extensively used in analysis of industrial wastes and wastewater.

30

COD measures pollution potential of an organic matter. Decomposable organic matter results in

consumption of DO.

COD does not differentiate between biologically degradable &nondegradable organic matter.

As a result, COD values are greater than BOD values and may be much greater when significant

amounts of biologically resistant organic matter are present (Sawyer and McCarty, 1978).

The COD concentration suitable for anaerobic treatment is generally a COD concentration

greater than 1500 to 2000 mg/L are needed to produce sufficentquentities of methane to heat the

wastewater without an external fuel source. At 1300 mg/L COD or less, aerobic treatment may

be the preffered selection".( Metcalf and Eddy(2004). "Organic Concentration and

Temperature"pg 987)

31

Chapter 3

3.0 Materials and methodology

3.1. Fieldwork

3.1.1. Reconnaissance

A preliminary visit to Karatina was made on 26th

March, 2014 to familiarize with the area and

establish a coffee processing factory for sample collection. It was agreed that the

Gatomboyacoffee factory would be the preferred site. An appointment with the manager was

made prior to the actual site visitation.

3.1.2. Descriptions of the Experimental Site

The experimental materials (coffee pulp and wastewater) were collected from Gatomboyawet

coffee processing factory, on 3rd

March, 2014, whereas the experimental process was undertaken

at the University of Nairobi, School of Engineering, Dept. of Civil and Construction Engineering

at the Public Health Engineering laboratory.

Gatomboya is located in Karatina, a small town in Nyeri County, Kenya, with a population of

6852 (1999 Census). It is 20km to the east of Nyeri town at an altitude of 1868m above sea level

and at a longitude of 36.767 degrees . The mean annual temperatures range from 12 to 27

degrees Celsius and the annual rainfall varies from 550mm to 1500mm. March to April

characterizes the small rainy season while the long rainy season extends from October to

December. Most of the coffee produce is realized during the long rainy season and thus large-

scale wet coffee mill process is carried out around the same time. Karatina lies on a plateau

directly below the southern side of Mount Kenya. It is fed radially by flowing streams running

from Mount Kenya towards the lower slopes of the mountain and is marked by Tana River, the

longest river in Kenya.

3.1.3. Site Visitation

A visit to Gatomboya Factory, a wet coffee processing factory, was carried out on 3rd

March,

2014. The plant manager, one Mr.Munene, guided the tour. Below is a case study of the

32

Gatomboya wet coffee processing mill giving a detailed description of the activities that took

place during the whole coffee wet process.

3.1.3.1 Case Study: Gatomboya wet coffee processing mill

Gatomboya factory is a wet coffee processing mill that serves the Barichu Farmers‟ Cooperative

Society, one of the many cooperative societies in Karatina. Gatomboya factory was an initiative

from localfarmers started in 1985 and has served farmers in the area since then. A study of the

wet coffee milling processwas conducted under the supervision of the plant

manager,Mr.Munene. The wet coffee milling process is a sequential process operated manually

by a machine operator. During the large-scale processing, the whole processis monitored from a

computer while during the low season the process is monitored manually by sight observation.

The whole process has distinct stages from the coffee grading process to the waste collection

point.

Stage 1

In this stage, the farmers bring in their coffee berries which are graded to remove the bad berries.

Thebad berries are used as manures by the farmers. The good berries are weighed and then

emptied into the cherry hopper. See images below.

Fig 3.1 Grading coffee berries and the cherry hopper

33

Stage 2

The berries in the cherry hopper empty into the pulping unit by gravity. The pulping unit consists

of the pulping machine. Here the pulp is separated and removed from the coffee bean by the

running water in the pulping machine. The pulping machine is operated by electricity. The flow

of water also separates the beans into different grades. See the image below.

Figure 3.2 Pulping machine

Figure 3.3 Coffee pulp separated

Stage 3

The coffee bean that has been separated from the pulp is driven by the water to the fermentation

tanks. Here the beans are allowed to ferment for about 45 hours or less depending on the time it

takes the remaining layer surrounding the bean to clear off. The beans are then washed twice and

taken by the flowing water to dry in the drying cable as shown in the images below:

34

Figure 3.4 Fermentation tank

Figure 3.5 Drying cables

Once dry the beans are taken to the bean shed and the store where they are packed in 50kg bags.

The waste water from the coffee processing is recycled in the recirculation pump house by a

pump and used over and over again till it cannot be used anymore and the dumped in the soak

pits. The pulp is dumped directly into the soak pit. See images below.

35

Figure 3.6 Recirculation pump house

Figure 3.7 Soak pit

3.1.4. Sample Collection

Fresh wet coffee processing waste (pulp and wastewater) was collected in plastic bottles and an

open plastic container respectively and kept fresh in an icebox ready for laboratory testing.

3.2. Methodology and materials for determination of BOD of the sample

Objective: To determine the Biochemical Oxygen Demand – BODu and BOD5 – of a given

sample of coffee wastewater

Apparatus and Reagents

Reagents

36

For dilution water:

Phosphate buffer solution

Ferric chloride solution

Magnesium sulphate solution

Calcium chloride solution

For dissolved oxygen determination by azide modification:

Manganoussulphate solution

Concentrated sulphuric acid

Starch indicator solution

Standard sodium thiosulphate solution 0.025

Apparatus

Burettes

Pipettes

BOD bottles

Beakers

Conical flasks

Procedure

1) 6 litres of dilution water was made up by adding:

6 ml of phosphate buffer solution

6 ml of ferric chloride solution

6 ml of magnesium sulphate solution and

6 ml of calcium chloride solution

to 6 litres of distilled water kept aerated in the aspirator bottle. The solution was mixed

well and aeration continued.

2) 2 samples A and B were used (sample A being wastewater in soak pits after 3 months,

sample B(coffee pulp in soak pits fresh from being depulped).The volume of the sample

to be taken in each bottle which when filled with dilution water would result in dilutions

of 1:10, 1:25, 1:50, 1:100 for samples A and dilutions of 1:100, 1:140, 1:200, 1:280 for

sample C.

37

3) Four sets of BOD bottles each set containing three bottles were arranged and labeled with

the dilution factors mentioned above

4) Calculated amounts of sample were transferred to each bottle as appropriate.

5) The bottles were then filled with dilution water without overflowing and stoppered

without trapping any air-bubbles.

6) Another set of three bottles were taken, identified as dilution water blank and then filled

as before with dilution water without any sample.

7) The dissolved oxygen concentration was determined in one bottle from each of the five

sets of bottles as follows:-

a) The stopper was removed and in quick succession 2 ml each of

manganoussulphate solution and alkali azide-iodide reagent added, with the tip of

the pipette well below the water level in the bottle. The stopper was again

replaced taking care not to trap any air bubbles.

b) The contents of the bottle were mixed by inverting the bottle several times and

letting the precipitate settle half-way down the bottle. The contents were mixed

again and the precipitate allowed to settle as before.

c) 2 ml of concentrated sulphuric acid was added using a bulb, to the contents of the

bottle, with the tip of the pipette just below the water level. The stopper was then

replaced and the content mixed again till all the precipitate had dissolved.

d) 203 ml of solution was measured from the bottle and transferred to an erlenmeyer

flask. The solution was then titrated against standard sodium thiosulphate solution

till the color changed to pale yellow. About 1 ml of starch indicator solution was

then added. Titration was continued till the blue color disappeared.

8) The remaining bottles were incubated at 20oC for four days in the incubation cabinet.

9) The dissolved oxygen concentration in each bottle was determined in each bottle at the end

of the incubation period.

38

3.3. Methodology and materials for determination of COD of the sample

COD test is a measure of quantity of oxygen required to oxidize the organic matter in a

wastewater sample, under specific conditions of oxidizing agent, temperature and time. COD test

is extensively used in analysis of industrial wastes and wastewater.

COD measures pollution potential of organic matter. Decomposable organic matter results in

consumption of DO.

COD does not differentiate between biologically degradable &nondegradable organic matter.

As a result, COD values are greater than BOD values and may be much greater when significant

amounts of biologically resistant organic matter are present (Sawyer and McCarty, 1978).

Reagents:

Distilled water

Standard potassium dichromate solution, 0.025N

Sulphuric acid concentrated reagent containing silver sulphate

Standard ferrous ammonium sulphate (FAS), 0.025N

Powdered mercuric sulphate

Phenanthroline ferrous sulphate (indicator)

Apparatus:

Reflux apparatus with ground glass joint

250ml Erlenmeyer flask with ground glass joints

Pipettes

Procedure:

1. 20ml of the sample was placed in 250 ml refluxing flask.

2. 1gm of mercuric sulphate, several glass beads were added into the solution. 5ml of H2SO4

(concentrated sulphuric acid) was added slowly while mixing to dissolve the mercuric

acid.

3. The sample was mixed while cooling to avoid possible losses of volatile materials.

39

4. 25ml of 0.0471M K2Cr2O7 solution was added and mixed thoroughly.

5. The samples were then transferred to the Liebig condenser apparatus. The remaining

sulphuric acid reagent (70ml) was then added through the open end of the condenser.

6. The samples were continuously stirred while adding the acid reagent.

7. The reflux mixture was mixed thoroughly by applying heat to prevent local heating of the

flask bottom and a possible blow out of the flask contents.

8. The open end of the condenser was covered with a foil to prevent foreign materials from

entering the refluxing mixture.

9. Refluxing was then carried out for 2hours.

10. The condenser was thereafter cooled and washed down using distilled water.

11. The reflux was then disconnected and diluted to about twice its original volume with

distilled water.

12. This mixture was then cooled to room temperature (due to the exothermic nature of the

reaction). The excess K2Cr2O7 was then titrated using FAS using 0.1-0.15ml (2 to 3

drops) ferroin indicator.

13. The same volume of ferroin indicator was used for all titrations.

14. The end point of the reaction was taken as the first sharp change in colour, from blue-

green to reddish brown.

15. Similarly a blank of equal volume to sample, distilled water was titrated against FAS.

40

Chapter 4

4.0 Results, analysis and discussion

4.1 BOD results and analysis

4.1.1 Result

Sample A (coffee wastewater in soak pits after 3months)

Dissolved Oxygen Concentration before Incubation

Blank………………7.9 ml

1:100………………7.5ml

1:50………………..7.4ml

1:25………………..7.1ml

1:10………………...6.0ml

Dissolved Oxygen Concentration after Incubation

Blank……………….7.4 ml

1:100………………..6.3 ml

1:50…………………6.2 ml

1:25…………………6.1 ml

1:10…………………all oxygen was used up

Sample B(coffee pulp in soak pits fresh from being depulped.)

Dissolved Oxygen Concentration before Incubation

1:280…………………6.6 ml

1:200…………………6.5 ml

1:140…………………6.4 ml

1:100…………………6.3 ml

Dissolved Oxygen Concentration after Incubation

1:280………………….5.8 ml

1:200………………….5.6 ml

1:140………………….5.4 ml

41

1:100………………….all oxygen was used up

BOD5

Sample A

1:10 = 120 mg/l

1:50 = 60 mg/l

1:25= 25 mg/l

1:10 : all the oxygen was used up before day 5

Average BOD5 = 68.3 mg/l

BODu = 173.6mg/l

Sample B

1:280 = 224 mg/l

1:200 = 180 mg/l

1:140 = 140 mg/l

1:100 : no oxygen was left after day 5 of the experiment

Average BOD5 = 181.3 mg/l

BODu = 460.8mg/l

4.2 COD results and analysis

4.2.1 Results

Sample A (coffee pulp in soak pits after 3months)

CODA= 164 mg/l

Sample B (coffee pulp in soak pits fresh from being depulped.)

CODB= 368 mg/l

42

4.3 BOD/COD ratio (biodegradability, αs)

Biodegradability of sample, αs = BOD 5

COD

Sample A αs = 0.41

Sample Bαs = 0.49

4.4 Discussion The Biochemical Oxygen Demand theoretically takes an infinite time to be completed because

the rate of oxidation is assumed to be proportional to the amount of organic matter remaining.

Within the 5-day period used for the BOD test, oxidation is from 60 to 70 percent complete.

From the test results it can be realized that the BOD of the sample increases with an increase in

dilution of the samples. Also, it can be noted that highly concentrated samples tend to deplete

their oxygen faster than less concentrated samples as evidenced by the most concentrated

dilutions of samples A(1:10 dilution) and C(1:100 dilution) whereby after 5 days the sample

turned white indicating that all the oxygen has been used up.

The Chemical Oxygen Demand of the samples A and B were found to be higher than the BOD

values of the same samples. COD values are always higher than BOD values because COD

includes both biodegradable and non-biodegradable substances while BOD contains only

biodegradable substances.The considerations for the AD Process include the following

application Ranges:

< 50mg/l COD à carbon absorption

50 < 4000mg/l COD à Aerobic Digestion

It should also be noted that the biodegradability value of sample A and B are 0.41 and 0.49

respectively. BOD/COD ratio of 0.4 and above is considered to be biodegradable (Gilbert,

1987)hence so for the above samples.

43

Chapter 5

5.0 Conclusion and recommendations

5.1 Conclusion

Focusing only on COD removal, low concentration even < 100 mg/L would be okay for the

production of biogas. The COD value of 368mg/l provides apreliminary indication of the biogas

generation potential

The values of COD ( 164mg/l and 368mg/l), BOD (173.6mg/l and 181mg/l) determine the

BOD/COD ratios mentioned above infer that the above samples are biodegradable and are

potential source of biogas. According to Kivaisi, et.al, coffee wastewater has a biogas potential

of 375m3/ton CODrem which is a very high value of energy production hence further concluding

that Gatomboya coffee factory is a potential source of bioenergy.

5.2 Recommendation

The following are recommendations with regard to the findings of this research:

More research should be undertaken to determine the amount of biogas that can be

generated from an exact amount of coffee pulp.

44

REFERENCES

Abebe Belay, KassahunTure, MesfinRedi and Araya Asfaw, 2008. Measurement of caffeine in

coffee beans with UV/spectrometer. Journal of Food Chemistry, 108: 310-315

Adams, M.R. and J. Dougan. 1987. Green Coffee Processing.. In: Clarke, R.J.and R. Macrae,

ed., Coffee. Volume 2: Technology. New York, NY: ElsevierScience Publishers, pp. 257 – 291

Agro Industrial Biomass in Kenya. German Biomass Research Centre (2010)

Boopathy, R., 1988. Dry anaerobic methane fermentation of coffee pulp. J. Coffee Research , 18:

59-65

Coffee and Health.Thecoffeefaq.com (2005-02-16).Retrieved on 2014-01-22.

Cornelis, MC; El-Sohemy, A (2007). "Coffee, caffeine, and coronary heart disease". Current

Opinion in Clinical Nutrition and Metabolic Care

DEVI, R., SINGH, V. y KUMAR, A.: “COD and BOD reduction from coffee processing

wastewater using Acavadopell carbon” Bioresour. Technol., 99: 1853-1860, 2008.

Gilbert, E. "Biodegradability of ozonation products as a function of COD and DOC elimination

by example of substituted aromatic substances." Water Research 21.10 (1987): 1273-1278.

George Tchobanoglous, et al., Wastewater Engineering: Treatment and Reuse, 4th Edition,

Metcalf & Eddy, Inc, pp 88-91.

http://en.wikipedia.org/wiki/Coffee#World_production

http://en.wikipedia.org/wiki/Coffee#Production

Kida K., M. Teshima, Y.Sonoda, K. Tanemura (1994), Anaerobic digestion of coffee waste by

two-phase methane fermentation with slurry-state liquefaction, Journal of. Fermentation

Bioengering , 11: 335-339

Kivaisi A.K. and Rubindamayugi M.S.T.: The potential of agro-industrial residues for

production of biogas and electricity in Tanzania. WREC-IV World Renewable Energy Congress,

Bd. 9, (1-4) S. 917-921, 1996.

Malina J.F. &Pohland F.G., Design of Anaerobic Process for the Treatment of Industrial and

Municipal Waste (TD755.D457)

Sawyer, C.N. and P.L. McCarty. 1978. Chemistry for Environmental Engineering.

McGraw-Hill Book Company, New York.

45

Wildenborg T and Lokhorst A (2005) Introduction onCO2 Geological storage-classification of

storageoptions. Oil Gas Sci. Technol. Rev. 60, 513–515.

www.giz.de/facheexpectise/..gtz2010-en-biogas-assessemt-kenya.(Agro-industrial Biogas in

Kenya.)

46

47

APPENDICES

Appendix A.4.1 BOD Calculations

5 – Day, 20oC BOD = (D1 – D2) / P mg/l

Where: D1 = DO in diluted sample before incubation

D2 = DO in diluted sample after incubation

P = decimal fraction of the sample in the BOD bottle

BODu= BOD 5

1−e−kt

Where: k = 0.10 day-1

t = 5days

Decimal fractions of samples (P)

Pblank = 0.00

P1:280 = 0.0036

P1:200 = 0.005

P1:140 = 0.0071

P1:100 = 0.01

P1:50 = 0.02

P1:25 = 0.04

P1:10 = 0.1

BOD5

Sample A

1:100 = 7.5−6.3

0.01 = 120 mg/l

48

1:50 = 7.4−6.2

0.02 = 60 mg/l

1:25 = 7.1−6.1

0.04= 25 mg/l

1:10 : all the oxygen was used up before day 5

Average BOD5 = 120+60+25

3 = 68.3 mg/l

BODu= 68.3

1−e−0.10 ×5 = 173.6mg/l

Sample B

1:280 = 6.6−5.8

0.0036 = 224 mg/l

1:200 = 6.5−5.6

0.005 = 180 mg/l

1:140 = 6.4−5.4

0.0071 = 140 mg/l

1:100 : no oxygen was left after day 5 of the experiment

Average BOD5 =224+180+140

3 = 181.3 mg/l

BODu= 181.3

1−e−0.10 ×5 = 460.8mg/l

49

Appendix A 4.2 COD Calculations.

COD in mg/L = a−b ×m × 8000

ml of sample

Where:

a = ml, of titrant used for blank water

b = ml, of titrant used for sample water

m = molarity of the FAS

Sample A (coffee wastewater in soak pits after 3months)

CODA = 242−19.8 ×0.1 ×8000

20 = 164mg/l

Sample B (coffee pulp in soak pits fresh from being depulped.)

CODC = 25.2−16.0 ×0.1 ×8000

20= 368 mg/l

Appendix A4.3 BOD/COD ratio (biodegradability, αs)

Biodegradability of sample, αs = BOD 5

COD

Sample Aαs = 68.3mg /l

164mg /l= 0.41

Sample Bαs = 181.3mg /l

368mg /l= 0.49